In the prior art, there are several minor and casual references to processes for activating CuO/ZnO/Al.sub.2 O.sub.3 catalysts. Among those references having a major relationship to the activation of CuO/ZnO/Al.sub.2 O.sub.3 catalysts are the following:
U.S. Pat. No. 4,623,668 discloses the preparation of methanol by catalytic conversion of a synthesis gas mixture, containing hydrogen, carbon monoxide, carbon dioxide and/or water, at 200.degree.-320.degree. C. and under 30--300 barr, in adiabatic and/or isothermal reactors in the presence of a catalyst containing copper and zinc, by a process in which the fresh catalyst is initially reduced with a hydrogen-containing gas, and then the synthesis is started under conventional conditions and is continued until formation of methanol in the reaction zone has declined substantially, after which the reaction is interrupted and the catalyst is regenerated.
U.S. Pat. No. 4,639,470 discloses the preparation of methanol in a liquid phase methanol reactor by entraining a methanol-forming catalyst in an inert liquid and contacting said catalyst with a synthesis gas comprising hydrogen and carbon monoxide. The mention of catalyst activation is very casual and a detailed procedure is not given, however, activation is carried out in the gas phase and the catalyst is then transferred into the liquid phase reactor.
U.S. Pat. No. 3,701,739 discloses a heterogeneous catalyst which is formed by decomposing and partially dehydrating an ammoniacal solution of a mixture of the carbonate or hydroxide of at least one metal which is reducible in hydrogen and carbonate or hydroxide of at least one metal which is nonreducible in hydrogen in a fluid bed. Residual volatiles are removed from the resulting fine particle agglomerates of the metal oxides under conditions which prevent grain growth. Afte pelletizing the composite material, it is treated with hydrogen at relatively low temperatures to reduce one or more of the oxides to its metal which remains dispersed in the remaining oxide or oxides. The catalyst thus formed has a large effective surface area and remains effective over a prolonged period of time.
U.S. Pat. No. 3,546,140 discloses a process for the preparation of a low temperature shift catalyst. The conditions for activation are disclosed in column 3 of the patent which states that "the catalyst was first reduced by treatment for about 8 hours at 500.degree. F."
U.S. Pat. No. 3,850,850 discloses a catalyst precursor which is made by forming a first precipitate comprising oxides capable of reacting together to form a mixed oxide having a spinel structure, forming a second precipitate comprising a copper compound decomposable to oxide, and mixing the two precipitates. Such a precursor may after reduction be used as a methanol synthesis catalyst capable of long-term use at high levels of catalytic activity.
U.S. Pat. No. 4,535,071 discloses a catalyst for methanol synthesis which contains (a) as catalytically active substances copper oxide and zinc oxide, which, if desired, may be at least partially reduced and (b) as a thermal stabilizing substance aluminum oxide. The proportion of pores with a diameter of 20-75 angstroms (mesopores) is at least 20% and the proportion of pores with a diameter greater than 75 angstroms (macropores) is at the most 80%. The desired pore distribution can be obtained by using colloidally dispersed aluminum oxide or hydroxide in the production of the catalyst.
U.S. Pat. No. 4,436,833 discloses a process for the preparation of methanol by reacting a gaseous mixture of carbon monoxide, carbon dioxide and hydrogen at an elevated temperature and pressure over a catalyst which contains zinc, copper, and aluminum. The catalyst is prepared from a co-crystalline material of the formula: EQU Cu.sub.2.2 Zn.sub.2.8 (OH).sub.6 (CO.sub.3).sub.2
containing aluminum hydroxide as a structural promoter, by calcination and reduction from 160.degree.-350.degree. C. The novel catalyst has an advantage of giving a substantially increased space time yield and having a longer life.
U.S. Pat. No. 3,922,694 discloses a methanol synthesis catalyst precursor which comprises copper oxide and a support comprising spinel-forming metal oxides, spinel being present in crystallites not larger than 120 angstroms. Using catalyst prepared from such a precursor by reduction, methanol synthesis can be operated without changing catalyst for longer periods than when using a similar catalyst containing no spinel. A precipitation method for making the precursor is also disclosed.
U.S. Pat. No. 4,547,482 discloses a catalyst composition having copper oxide, zinc oxide, and an oxy-acid of phosphorus or its salt; and a method for producing methanol by reacting carbon monoxide and/or carbon dioxide with hydrogen in the vapor phase in the presence of a catalyst, wherein the catalyst is the aforesaid catalyst composition which has been activated by gas-phase reduction with a hydrogen-containing gas.
U.S. Pat. No. 4,477,594 discloses a process for the synthesis of mixtures which include saturated aliphatic alcohols. In the first step of the process, a catalyst, which comprises the oxides of copper, zinc, aluminum, potassium and one or more additional metals selected from the group consisting of chromium, magnesium, cerium, cobalt, thorium, lanthanum, is partially activated. In this step a reducing gas stream, which includes hydrogen and at least one inert gas, flows past the catalyst at a space velocity of up to 5,000 standard liters per hour, per kilogram of catalyst. The partially activated catalyst is then subjected to the second step of the activation process. In this step the catalyst is contacted by an activation gas stream comprising hydrogen and carbon monoxide present in a volume ratio of 0.5 to 1 and 4 to 1, respectively, at a temperature of 200.degree.-450.degree. C. and a pressure of between 35-200 atmospheres. The activation gas flows at a space velocity of about 1,000-20,000 standard liters per hour per kilogram of catalyst. Second stage activation continues until the catalyst is contacted with at least 500,000 standard liters of activation gas per kilogram of catalyst. The fully activated catalyst, in the third step of the process, contacts the synthesis gas stream comprising hydrogen and carbon monoxide.
U.S. Pat. No. 4,537,876 discloses a method for activating a methanol synthesis catalyst. In this method, the catalyst is slurried in an inert liquid and is activated by a reducing gas stream. The activation step occurs in-situ. That is, it is conducted in the same reactor as the subsequent step of synthesizing methanol from a methanol gas stream catalyzed by the activated catalyst still dispersed in a slurry.
Except for U.S. Pat. No. 4,537,876, the above references utilize a gas-phase reduction/activation step, however, all of the references share a common characteristic: there is no recognition of the relationship between the catalyst temperature and hydrogen consumption, and the criticality of this relationship in determining whether the catalyst is properly activated.